Supplemental thread tension for sewing machines



y 1953 D. sE cREs T 2,645,

SUPPLEMENTAL THREAD TENSION FOR SEWING CRIMES Filed Aug. 30, 1949 Patented July 14, 1953 SUPPLEMENTAL THREAUTENSI/ON FOR SEWING MACHINES Levi Douglas Secrest, Santa Ana, Calif. Application August 30, 1949, SerialNo. 113,060:

This invention relates to improvements in thread tensioning devices for sewing machines, and has particular reference to a thread tension for the type of sewing machine commonly used for sewing up filled bags, although the invention is not confined to such use, being adapted for use on machines ofother types and for other purposes. Reference is made to my abandoned application, Seria1 No. 445,491, filed June 2, 1942, containing related subject matter.

It is a general object of my invention to provide thread tensioning means for a sewing machine which will permit much tighter sewing than heretofore has been possible without risk of breaking the thread or of dropping stitches.

A further object of the invention is to provide a thread tensioner which may be applied to practically all existing types of sewing machines,

which never needs adjustment, can not get out oforder, and may be threaded quickly and easily.

I am aware that thread tensioning devices have been used for many years upon sewing machines, and purportedly to accomplish the abovestated object of permitting tight sewing. Sewing machines are also commonly provided with devices properly termed thread-controllers, the function of which is to takeup slack in the thread and which are therefore often confused with thread-tensions. The distinction between a thread-tension and a thread-controller may be stated as follows: a thread-tension offers a resistance to movement of the thread, tensing the portion of the thread between the threadtension and whatever element exerts a pull on the thread; a thread-controller acts by relative movement with respect to eyelets or thread-tensions defining a path for the thread, to extend or to decrease the length of the path so as to take up slack in the thread or to permit slack to de--' velop. A thread-tension may or may not be on v a moving element of the sewing machine; "a thread-controller always has relative movement with respect to adjacent thread-guidesalth'ough it may be a mere movable eyelet.

In most machines for sewing bags, thethread is guided from the spool to a thread-tension mounted on a stationary portion of the machine, the purpose of which is to restrict the length of thread pulled from the spool by each movement of the needle-bar to substantially the precise length needed for the next stitch. Between the aforesaid thread-tension and the eye of the needle, the thread may be guided by one or more eyelets, one of which is usually on or in the needle-bar. As the needle-bar reciprocates, the path of the thread between the aforesaid threadtension and the needle-bar eyelet is changed in shape and length, alternately producing slack in the thread and tightening the thread to pull more thread from the spool. To control the 2 Claims. (01. 1124.54)

hack, unread-commoner is usually inserted in this portion of the thread-path, and is operated either by movement of the needle-bar or presser barorby movement of the needle-bar'lever to swing arcuately in such a manner as to maintain tension on the'thread or to yield slack thread to the needle as may be required. For example, on the forward or penetrating stroke of the needlebar, the thread-controller may be actuated'to move in a direction elongating the path of the thread, and thereby pulling the thread back through the needle eye so that the slack thread beyond the needle eye forms a smaller and more accurately placed loop. The thread is pulled back through the needle eye because the frictional resistance at the needle eye and at the needle-bar eyelet is less than at the initial thread-tension on the other side of the threadcontroller. On the next rearward stroke of the needle-bar the thread-controller will be actuated to move in a direction shortening the path of the thread between the initial thread-tension and the needle-bar eyelet, thus providing some slack in the thread at this part of the path. Thi slack is pulled through the needle eye by the previously formed stitch to provide loop thread for the next stitch.

It will be apparent from the foregoing description of a conventional sewing machine action that, the thread tends to be slack between the initial thread-tensionand the needle at the. moment when the previously formed stitch is being pulled to its ultimate tightness. If, by reason of very careful adjustment of the thread controller, slackness does not occur, still the tension is distributed over the quite substantial length of thread from the work to the initial thread tension. To give this length of thread adequatetension to produce tight stitches and yet not exceedthe breaking tension when the thread-controller moves to increase the tension requires very accurate adjustment; and infactoryoperations where the machines are in con: stant use sewing thousands of bags and are consequently subject to much wear and resultant looseness of operation, the servicing time required to maintain a balance between loose stitching and broken threads may seriously affect the machine output.

It is accordingly a more detailed object of my,

invention to provide thread tensioning means supplemental to the conventional thread tension which will maintain that portion of the thread closely proximal to the needle at a tension suitable for tightening the stitches during the stitchtightening movement of the needle.

It is another detailed object of my invention to provide thread tensioning means which in part relieve the conventional thread-controller of the function of removing slack from the thread during the stitch-tightening operation so that improper adjustment of the thread-controller is less likely to result in broken thread.

Further objects and advantages of my invention will either be specifically pointed out as the following description of a preferred embodiment of the invention proceeds, or will be apparentfrom consideration of that description and of the accompanying drawing, illustrative thereof, in which:

Fig. 1 is a fragmentary elevational view of a portion of a sewing machine, showing my supplemental thread-tension applied thereto in a preferred location and manner; 7

Fig. 2 is an elevational view on an enlarged scale of a portion of the assembly shown in Fig. 1, illustrating the action of my supplemental thread-tension in response to movement of the needle of the sewing-machine in its retractive stroke; 7

Fig. 3 is a View similar to Fig. 2, illustrating the action of my supplemental thread-tension during the forward or penetrating stroke of the needle; and

Fig. 4 is a plan view of a preferred form of my supplemental thread-tension.

Having reference now to the details of the drawings, I have shown in Fig, 1 the goose-neck I of a conventional sewing machine adapted and disposed for horizontal sewing n the mouths of filled bags, which it will be understood pass under the goose-neck in erect position to have their mouths closed and stitched. Pivoted to the goose-neck 1 at a pivot 8 is the needle-bar rocker arm or lever 9 which is oscillated by wellknown means not shown and which through linkage indicated at l0 causes a needle-bar H to reciprocate in guides 12, as shown in Figures 2 and 3. The thread l3, on such a machine,

is usually trained through one or more eyelets M on its path to an initial thread-tension l5 and then follows an irregular path .of variable length between the initial tension I5 and the eye of a needle, not shown, carried by the needlebar H. A thread-controller l6 is pivoted on the oose-neck "I at H, so .asto be arcuately oscillated by a rack [8 or equivalent attachment operated .reciprocatively by the needle-bar or by a presser-foot.

In the type of machine herein illustrated, the path of the thread between the tension and the eye of the needle is usually defuied by an eyelet on the rocker arm 9, an eyelet 21 on the thread-controller 6, a second eyelet 22 on the rocker-arm 9, and an eyelet 23 on the needle bar ll. As the linkage and mechanical action of the machine is such that the eyelet 2| moves to the left when the eyelets 20, 22, and 23 move to the right, the length of thread required between the eyelets 20 and 23 is constantly expanded and contracted, as hitherto described. It will be obvious that, although the length of the thread-path varies and the thread may be alternately slack and tensed, the amount of tension when the thread is tensed will depend, in the absence of additional tensioning devices, upon the resistance to movement of the thread produced at one end of the path by the initial thread-tension l5 and at the other end of the path by the loop or stitch in the work being sewn.

To better control the tension upon the thread and also to take up and to yield slack thread in the manner of a thread-controller, I mount a supplemental thread-tension 25 on the machine between the eyelets 22 and 23. The sup.-

plemental thread-tension 25 may be mounted on either a stationary or a moving part of the machine, but as the eyelets 22 and 23 both move to the left and to the right simultaneously, thus changing the length of the path from the one to the other passing through a stationary point between them, I find it convenient to mount the supplemental tension 25 in stationary position on the end of the needle-bar guide frame 12 at a point between the ends of the reciprocating stroke of the needle-bar II. This position, in addition to having relative movement with respect to the eyelets on opposite sides of it, has the advantage of being very close to the eyelet 23 at all times. I have found that the effectiveness of my supplemental tension is increased when it is placed as close as possible to the work.

The supplemental tension 25 may have various forms, it being requisite for its satisfactory operation merely to have a post, spool, or like device around which sufficient turns of thread may be looped to create a snubbing force by friction when the thread is pulled around it. A preferred form of tension, which I have found very satisfactory is shown in Fig. 3 and comprises a wire post 26, adapted to be inserted in a suitable hole in the guide frame I 2 and bent laterally at its outer end and then wound in a spiral 21 in returning circumvolutions around the post 26. The thread I3 is wound upon the post 26, with the coils of the thread separated by the coils of the spiral 21. The requisite snubbing friction is thus generated between the post 26 and the coils of the thread, which may be one or more r as needed, the spirals 21 serving only as separators to prevent the coils of thread from binding one upon another.

Operation When the needle bar H moves forward on its penetrating stroke, the thread-controller I6 is moved, as usual, to elongate the path of the thread between the eyelets 20 and 22, the eyelet 2! on the thread-controller moving to the left, as seen in Figure 1. As the eyelets 20 and 22 are on the needle bar lever which moves to the right during this phase of operation, the path of the thread from 20 to 22 is substantially elongated, and if this elongation takes up all the slack in the thread between 20 and 22, as it normally will, additional thread .must be drawn from some supply to meet the requirements of the new thread path. This additional thread will be drawn from the spool in part, thus supplying thread for additional stitching, and in part from slack thread between the supplemental tension 25 and the work. Slack thread is available from beyond the supplemental tension 25 and may be pulled back to meet the requirements of the new path 20-22, because the needle bar eyelet moves forward from 2311 to 23b (see Figure 2), temporarily shortening the distance between the supplemental tension 25 and the needle bar eyelet and releasing the snubbing strain upon the supplemental tension. As the needle bar eyelet moves still further forward to 230, the snubbing strain is reimposed upon the supplemental tension, but lightly, slack thread beyond the needle eye being still available and being free to run rearward through the needle eye and the needle bar eyelet. During this phase of operation, the loop at the end of the needle is shortened, as heretofore described in connection with conventional machine operation. Because the supplemental tension is disposed close to the needle-bar eyelet, the relative movement between them is sufficient to cause the supplemental tension to act to some extent also as a supplemental thread-controller, supplementing and increasing the efficiency of the standard thread-controller.

When the needle-bar ll again moves rearwardly, in the direction of the arrow in Figure 4, the thread-controller It will swing back so as to shorten the path between the eyelets 20 and 22 and permit the thread to slack. This slack is soon taken up by the retractive movement of the needle-bar, and the thread will tighten upon the supplemental thread-tension. Towards the end of the retractive stroke of the needle-bar, the snubbing effect of the supplemental tension is sul'liciently great that thread must be retracted from the needle-eye. Consequentl a strong pull is developed upon the stitch just made, and tight sewing results. The condition of the thread when the needle-bar eyelet is at the successive retractive positions 230,

231),- and 23a, is shown, with some exaggeration, at I30, 13b and 13a, respectively, Figure 4. The pull upon the thread is developed gradually, with increasing force, minimizing the danger of breaking the thread. The pull is exerted upon a relatively short length of thread, increasing its effectiveness in tightening the stitch. Additional thread will be pulled through the initial thread-tension IE to ease the strain if the pull upon the thread develops sumcient force.

In the needle-retracting phase of operation just described, the thread-controller I6 operates to reduce the snubbing effect of the initial thread-tension l5, thereby permitting thread to be pulled from the supply, while the supplemental thread-tension 25 develops an increasing snubbing elfect because of the increasing pull of the tightening stitch. It will be apparent that the supplementary thread tension does not, in this phase of operation, materially affect the tightness of the thread extending rearwardly from it to the initial thread-tension l5, and it will normally be found that the ratio of the new thread pulled from the spool on the two strokes of the needle is about the same as in conventional operation, namely, about 10 per cent new thread on the forward stroke of the needle, and 90 per cent on the rearward stroke.

The supplemental tension does, however, af-

feet the tightness of the thread between itself and the work. In conventional operation-rthat it, in the absence of a supplemental tension disposed close to the needle-bar-the path from the eyelet 22 to the needle-bar eyelet 23 changes very little in length. The new thread path from the eyelet 22 to the supplemental tension 25 also changes very little in length, but the new thread path from the supplemental tension to the needle-bar eyelet 23 and thence to the Work changes radically in proportion to its length. In this sense, the supplemental tension again performs the function of a thread-controller as described and defined earlier in this specification.- But it obviously has added functions not to be performed by any thread-controller or mere eyelet, for a mere eyelet disposed on the guide frame would merely counteract the action of the thread-controller l6 and would permit distribution of the resultant tightness or slackness of the thread all the way from the thread-tension l5- to the work, while the thread-tension of my invention, disposed at the same point, in no way counteracts the action of the thread-controller 16 but provides a highly desirable tightness of during the middle part of each stroke, one coil of thread might easily cross another and bind thereon, in the absence of separating means such as the spirals 21.

Obviously, my invention is subject to some modifications in form and in placement in its application to various types of sewing machines, hence I do not wish to be limited to the exact showing of the above-described example, but rather only to the scope of the appended claims.

I claim:

1. In a sewing machine: a needle-carrying.

bar, endwise reciprocable; a thread guide on said bar, distinct from the eye of the needle; and a thread-tension from which the thread leads directly to said thread guide and thence to the eye of the needle, comprising a membersecured against rotation relatively to said machine upon which the thread may be wound in at least one full coil to provide a snubbing resistance to passage of thread, and having coil-separating means for separating the on-coming and out-going portions of said thread upon said thread-tension; said thread-tension being mounted upon said machine between the limits of reciprocation of said thread guide and close to said bar, the shortest thread path from said thread-tension to said thread-guide being substantially shorter than the thread-paths existent therebetween when said thread-guide is at either of its limits of reciprocation. V

2. In a sewing machine: a needle-carrying bar endwise reciprocable; a thread-guide on said bar from which the thread is extended to the needle; and a thread-tension carried by said machine close to said bar and having a post extending transversely of the thread path to said thread guide and adapted to have the thread coiled thereon, the thread then extendingv directly from said thread-tension to said thread-' guide, the angle between the shortest path from said thread-tension to said thread-guide and the actual path therebetween increasing substantially as said thread guide approaches its limits of its reciprocation; said thread-tension being secured against rotation and including means defining a spiral path for thread wound upon said post for preventing adjacent coils of thread from overlapping.

LEVI DOUGLAS SECREST.

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